Packet transmission/reception method and apparatus in wireless communication system

ABSTRACT

A method for simultaneously transmitting packets to one or more users in a wireless communication system includes: generating the packets which include length information and are to be transmitted to the one or more users; and simultaneously transmitting the generated packets to the one or more users. The length information includes information representing a unit of the length information and information representing lengths of the packets according to the unit.

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application No.10-2010-0022417, filed on Mar. 12, 2010, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relate to a packettransmission/reception method and apparatus in a wireless communicationsystem.

2. Description of Related Art

The throughput of wireless communication systems is not high enough tosupport various high-capacity multimedia services. Since multi-usersshare wireless resources, the data rate of wireless services sensed bythe users decreases remarkably. In this regard, research is conducted onvarious techniques to improve the throughput of a wireless communicationsystem for multi-users by increasing a bandwidth to expand wirelessresources shared by multi-users, or by implementing a desired beam forcommunication with each user while using wireless resources of the samebandwidth.

Since a medium access control (MAC) protocol of a wireless communicationsystem operates on the basis of carrier sense multiple access/collisionavoidance (CSMA/CA), resource waste may occur in a channel contentionprocess. In order to solve such a problem, an enhanced MAC protocoldefined by IEEE 802.11e has proposed a burst transmission scheme inwhich multiple MAC protocol data units (MPDUs) are transmitted at ashort inter-frame space (SIFS) during a transmission opportunity (TXOP)time when a transmission right for a wireless resource is acquired, andblock ACKs for the multiple MPDUs are received. Furthermore, IEEE802.11n has defined an aggregated MAC service data unit (MSDU)(hereinafter, referred to as A-MSDU) and an aggregated MPDU(hereinafter, referred to as A-MPDU). In this case, MSDUs and MPDUs(which are a transmission unit) may be respectively aggregated withoutIFS, and then transmitted through a one-time contention process for awireless resource.

With the development of the above-described wireless communicationsystem, IEEE 802.11ac specifies that, in order to construct a high-ratewireless communication system, a data rate of up to 1 Gbps should besupported by a MAC service access point (SAP) of an access point (AP) ina wireless communication system including one AP and two stations(STAs), and a data rate of up to 500 Mbps is required by a MAC SAP of anSTA for a point-to-point environment. Furthermore, as the requirementsof the high-performance wireless communication system, each AP and STAneed to support compatibility with the existing wireless communicationsystem (the IEEE 802.11a/n system).

In the wireless communication system, a data transmitter (AP or STA)acquires a wireless channel and then transmits data together withinformation required for the transmission of the data. A structureincluding the data and the information required for the datatransmission may be referred to as a packet. At this time, theinformation required for the data transmission is defined as a promisedvalue in a structure named ‘header’.

FIG. 1 illustrates the structure of a packet defined in IEEE 802.11a. Aprotocol header and data information of a previous stage, for example, aMPDU with a header and data of a MAC protocol is transmitted to areceiver, together with short and long training fields 110 and 120storing information required for a physical layer (PHY), a signal field130, a service field 142, and a tail & padding field 144, and thereceiver receives the data using information acquired from the receivedfields. At this time, the data included in a data field 140 as well asthe service field 142 and the tail & pad field 144 has a variable lengthwithin the maximum range. It is possible for the receiver to recognizethe length of the data through information stored in a length field 132of the signal field 130.

FIG. 2 illustrates the structure of a packet with a mixed format, whichmay be received both in an IEEE 802.11a system and an IEEE 802.11nsystem. Referring to FIG. 2, as the packet with a mixed format includeslegacy fields 210 such as a legacy-short training field (L-STF), alegacy-long training field (L-LTF), and a legacy-signal field (L-SIG),the IEEE 802.11a system may acquire information required for thereception of data. Furthermore, the packet includes fields 220 for theIEEE 802.11n system from an HT-SIG field such that the IEEE 802.11nsystem may acquire information required for the reception of data. Forexample, the IEEE 802.11a system uses length information stored in theL-SIG field, and the IEEE 802.11n system uses length information storedin the L-SIG field or information stored in a length field 222 in theHT-SIG₁, thereby recognizing the length of data.

As the packet structures as illustrated in FIGS. 1 and 2 are defined inthe IEEE 802.11a and 802.11n wireless communication systems, there is ademand for a packet structure suitable for a high-performance wirelesscommunication system (e.g., a wireless communication system based onmulti-user multi-input multi-output (MU-MIMO) technology), which iscapable of simultaneously transmitting different packets to multi-users,respectively.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to a method and anapparatus capable of simultaneously transmitting/receiving packetsto/from one or more users in order to satisfy requirements of ahigh-performance wireless communication system.

Other objects and advantages of the present invention can be understoodby the following description, and become apparent with reference to theembodiments of the present invention. Also, it is obvious to thoseskilled in the art to which the present invention pertains that theobjects and advantages of the present invention can be realized by themeans as claimed and combinations thereof.

In accordance with an embodiment of the present invention, a method forsimultaneously transmitting packets to one or more users in a wirelesscommunication system includes: generating the packets which includelength information and are to be transmitted to the one or more users;and simultaneously transmitting the generated packets to the one or moreusers, wherein the length information includes information representinga unit of the length information and information representing lengths ofthe packets according to the unit.

In accordance with another embodiment of the present invention, a methodfor receiving a packet from a transmitter which simultaneously transmitspackets to one or more users in a wireless communication systemincludes: receiving a packet including length information of the packet;and processing the packet using the length information of the receivedpacket, wherein the length information includes information representinga unit of the length information and information representing lengths ofthe packets according to the unit.

In accordance with another embodiment of the present invention, anapparatus for simultaneously transmitting packets to one or more usersin a wireless communication system includes: a packet generation unitconfigured to generate packets which include length information and areto be transmitted to the one or more users; and a transmission unitconfigured to simultaneously transmit the generated packets to the oneor more users, wherein the length information includes informationrepresenting a unit of the length information and informationrepresenting lengths of the packets according to the unit.

In accordance with another embodiment of the present invention, anapparatus for receiving a packet from a transmitter which simultaneouslytransmits packets to one or more users in a wireless communicationsystem includes: a reception unit configured to receive a packetincluding length information of the packet; and a packet processing unitconfigured to process the packet using the length information of thereceived packet, wherein the length information includes informationrepresenting a unit of the length information and informationrepresenting lengths of the packets according to the unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the structure of a packet defined inIEEE 802.11a.

FIG. 2 is a diagram illustrating the structure of a packet with a mixedform for an IEEE 802.11a system and an IEEE 802.11n system.

FIGS. 3 to 6 are diagrams illustrating the structures of packets in awireless communication system in accordance with various embodiments ofthe present invention.

FIG. 7 is a diagram illustrating the structure of a MAC A-MPDU frame inaccordance with an embodiment of the present invention.

FIG. 8 is a diagram illustrating the case in which the length of apacket is transmitted using a symbol number in a wireless communicationsystem for multi-users;

FIG. 9 is a diagram explaining a problem occurring in the case in whichthe length of a packet is transmitted using a symbol number in awireless communication system for multi-users;

FIG. 10 is a diagram explaining a problem occurring in the case in whichthe length of a packet is transmitted using a symbol number when thepacket is transmitted to a single user;

FIG. 11 is a diagram illustrating fields storing length information ofpackets in accordance with an embodiment of the present invention; and

FIG. 12 is a diagram illustrating the configurations of a packettransmitter and a packet receiver in accordance with an embodiment ofthe present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention.

The present invention relates to a method and an apparatus forsimultaneously transmitting/receiving packets to/from one or more usersin a wireless communication system. For the purpose of convenience,since the present invention is described based on a packet structure tobe used in an IEEE 802.11ac wireless communication system (also called avery high throughput (VHT) system), the present invention is not limitedto the name of a specific wireless communication system. Thus, thepresent invention can support various environments such as multi-channelenvironments (e.g., transmission/reception using frequencies differentfrom each other) and wireless LAN environments of a multi-usermulti-input multi-output (hereinafter, referred to as a MU-MIMO) system.Furthermore, it goes without saying that it is possible to supportvarious high speed wireless services based on the wireless communicationsystem proposed by the present invention.

FIG. 3 is a diagram illustrating the structure of a packet for an IEEE802.11ac wireless communication system in accordance with an embodimentof the present invention. The packet of FIG. 3 has a mixed format forcompatibility with 802.11a/n, and includes a field 310 for 802.11a/n,fields for 802.11ac, and a data field 340. The fields for 802.11acinclude a common field 320 for 802.11ac and a field 330 for each user of802.11ac. Here, the field 310 for 802.11a/n includes information to benotified to each user of 802.11a/n, the common field 320 for 802.11acincludes information to be commonly notified to multi-users of 802.11ac,the field 330 for each user of 802.11ac includes information to betransmitted to each of the multi-users of 802.11ac, and the data field340 includes data to be transmitted to each user. It is possible for an802.11ac system to acquire desired information through the field 310 for802.11a/n used for the existing wireless communication system, as wellas the fields 320 and 330 for 802.11ac. Furthermore, the field 330 foreach user of 802.11ac and the data field 340 may be provided to eachuser in different formats. For example, the configurations and/orlengths of sub-fields of the fields 330 and 340 may be set to bedifferent for each user.

Referring to FIG. 3, section (a) indicates a transmission length of thepacket transmitted for 802.11ac from the common filed 320, which storescommon information for all multi-users, to the data field 340, andsection (b) indicates a transmission length of the field 330 for eachuser of 802.11ac and the data field 340, except for the common filed 320commonly applied to multi-users. Information on the sections (a) and (b)may be included in a signal field (in the field 310) for legacy or thecommon filed 320 for 802.11ac according to the purpose of theinformation. Otherwise, the information may be included both in thesignal field 310 and the common filed 320.

The field 330 for each user of 802.11ac may include a training field(referred to as a ‘VHT training field’) and a signal field (referred toas a ‘VHT signal field’), as with 802.11a/n. Depending on whether a longtraining field (referred to as ‘VHT LTF’) of the VHT training field isresolvable or non-resolvable, the field 330 for each user of 802.11acmay be configured in a different manner with respect to each user. FIG.4 illustrates an example in which the VHT LTF is non-resolvable. In FIG.4, fields 330-1, 330-2 and 330-3 for each user of 802.11ac havedifferent lengths with respect to each user. Furthermore, data fields340-1, 340-2 and 340-3 may have the same data length or different datalengths with respect to each user. FIGS. 5 and 6 illustrate an examplein which the VHF LTF is resolvable. In FIGS. 5 and 6, fields 330-1,330-2 and 330-3 for each user of 802.11ac have the same length withrespect to each user. FIG. 5 illustrates an example in which data fieldshave the same length with respect to each user, and FIG. 6 illustratesan example in which data fields have different lengths with respect toeach user.

Referring to FIGS. 3 to 6, the 802.11ac packet requires a field fortransferring common information to each user and a field fortransferring different pieces of information to each user. Specifically,the existing 802.11a/n defines a byte-unit length. However, whensimultaneously transmitting packets with different lengths tomulti-users in accordance with the embodiment of the present invention,length information transferred to the multi-users should have differentvalues. In this regard, in order to efficiently control a VHT packet formulti-users, a method is required to appropriately inform each user ofdifferent pieces of information.

As described above, the IEEE 802.11 legacy MAC protocol of the wirelesscommunication system transmits data by the MPDU including an MSDU, whena transmission right for a wireless resource is acquired. The IEEE802.11 enhanced MAC protocol transmits data by the TXOP. Thehigh-throughput (HT)-MAC protocol of IEEE 802.11n transmits data by theA-MPDU. In the present invention, when a wireless system acquires atransmission right, the wireless system simultaneously transmits framesto multi-users based on the MU-MIMO technology. This is defined as anMU-MIMO transmission unit (an MU-MIMO TX unit) of the VHT-MAC protocol.

Furthermore, the VHT MAC protocol in accordance with the embodiment ofthe present invention may transmit a single MSDU or a MPDU. However,since the VHT MAC protocol should support throughput equal to or higherthan that of the HT-MAC protocol, the VHT MAC protocol may transmit anA-MPDU within a VHT frame. The method proposed in the embodiment of thepresent invention may be supported in both of the resolvable example andthe non-resolvable example, which have been described above.

FIG. 7 is a diagram illustrating the structure of a MAC frame includedin the data field 340 of the sections (a) and (b) illustrated in FIG. 3.Referring to FIGS. 4 to 6, when data has different lengths or the VHTLTF is non-resolvable, the transmission end times of packets for eachuser are different from each other. Consequently, when transmittingpackets with different lengths to multi-users, a pad of a MAC layer or aPHY layer is added next to data with a length shorter than the maximumtransmission length, thereby allowing transmission lengths for themulti-users to be equal to each other. FIG. 7 illustrates an example inwhich a MAC PAD 720 is added next to the final A-MPDU subframe 710-n inorder to allow the transmission end times of packets for multi-users tocoincide with each other.

The A-MPDU subframe 710-n defined in 802.11n includes one or more A-MPDUsubframes 710-1, 710-2, . . . , 710-n. Each of the A-MPDU subframes710-1, 710-2, . . . , 710-n may include a delimiter, a MPDU, and 0˜3pad. However, a 0˜3 pad 722 is not added to the final A-MPDU subframe of802.11n. The 0˜3 pad refers to a 0˜3 byte pad. Meanwhile, in the VHT,the 0˜3 pad 722 is added to the final A-MPDU subframe 710-n such thatall A-MPDU subframes including the final A-MPDU subframe can beprocessed in units of four bytes. In FIG. 7, this part is represented bythe ‘final A-MPDU subframe pad 722’. That is, it is necessary for theVHT system to maintain 4-byte alignment with respect to all A-MPDUsubframes including the final A-MPDU subframe. Next to the ‘final A-MPDUsubframe pad 722’, it may be possible to add null delimiters 724 ofwhich the MPDU length is ‘0’, which are necessary for coinciding thetransmission end times of packets with each other. The null delimiter724 may be the same as the null delimiter of 802.11n. Since the nulldelimiter 724 is 4 bytes, a 0˜3 pad (726: a final MAC pad) is added to apart which is not filled by the null delimiters 724. Similarly, the 0˜3pad refers to a 0˜3 byte pad.

The transmission length of a PPDU including the MAC A-MPDU for the VHTillustrated in FIG. 7 may be transmitted to each user as byte-unitlength information as with 802.11a or 802.11n, or as a symbol numberindicating data transmission duration. If the byte-unit lengthinformation is transmitted, a predetermined number of bits with aspecific length are required in order to indicate the transmission ofthe byte-unit length information.

Meanwhile, the ‘tail & pad’ fields 144 and 234 illustrated in FIGS. 1and 2 are positioned at the end of actually meaningful data transmittedto a user (a receiver), and is the final information of the data fields140 and 230, which is necessary for receiving and processing a packet atthe PHY layer of a user. For example, the tail field may be used forreturning a convolutional encoder to a zero (“0”) state, and the padfield may be used as dummy data for adjusting a preset size of a frame.

When the length information of a packet is transmitted as the symbolnumber, a smaller number of bits for length information are necessary ascompared with the case in which the byte-unit length information istransmitted. However, since it is not possible for the PHY layer of theuser to recognize the position of the final byte of meaningful data inthe packet received therein, it is not possible to recognize theaccurate position of the ‘tail & PHY pad’ field. In this regard, it isnecessary to position a ‘PHY pad & tail’ field at the end of a symbol inwhich the final data (e.g., MAC MPDU) exists. At this time, differentlyfrom the case in which a PHY pad field is positioned next to a tailfield in the existing wireless communication system (802.11a/n), thetail field may be positioned next to the PHY pad field (refer to FIG.8). In this way, even if the length information of a packet istransmitted as the symbol number, since the tail field is positioned atthe end of the final symbol, it is possible for a user to find the tailfield.

FIG. 8 illustrates an example in which the length of the packet isrepresented by the symbol number and the tail field is positioned at theend of the final symbol as described above. In accordance with theembodiment of the present invention, the length of the packet may befrom a service field 842 to a ‘PHY pad & tail field 846’, or from thecommon field 820 or the field 830 storing information to be transmittedto each user of the VHT to the ‘PHY pad & tail field 846’, asillustrated in FIG. 8.

A packet in the wireless communication system in accordance with theembodiment of the present invention may include fields 310 and 810 forlegacy, common fields 320 and 820 storing information to be commonlytransmitted to multi-users of the VHT, fields 330 and 830 storinginformation to be transmitted to each user of the VHT, and data fields340 and 840 transmitted to each user.

The field 810 for legacy may include a training field 812 and a signalfield 814 for legacy. The common field 820 for the multi-users of theVHT may include a signal field (822: VHT-SIGs) and a training field(824: VHT-TFs) which are to be commonly transmitted to the multi-usersof the VHT. The field 830 storing information to be transmitted to eachuser of the VHT may be a training field (VHT-TFs) for each user of theVHT, and may further include a signal field (VHT-SIGs) for each user ofthe VHT. The signal field for each user of the VHT may have a length of0˜n (n≧1) symbols and may be positioned at the front, intermediate orend of the VHT-TFs 830 illustrated in FIG. 8. That is, the signal fieldfor each user of the VHT may be positioned between the common field 820and the VHT-TFs 830, in the VHT-TFs 830, or between the VHT-TFs 830 andthe service field 842. The service field 842 of the PHY is positioned atthe frontmost portion of the data field 840 to be transmitted to eachuser, and may have a value ‘0’ of bits before being scrambled by ascrambler and be initialized to a pseudo-random nonzero seed value,similarly to the service fields 142 and 232 illustrated in FIGS. 1 and2. At this time, the scrambler nonzero seed value is represented by 9bits and remaining 7 bits may be reserved bits. The above-mentioned ‘PHYpad & tail field 846’ is added to the last portion of the data field 840to be transmitted to each user. In the embodiment, the ‘PHY pad & tailfield 846’ may be represented by one byte.

The VHT A-MPDU included in the data field 840 to be transmitted to eachuser may have a configuration as illustrated in FIG. 7. At this time, asillustrated in FIG. 9, when the length of data 710 for a single user (afirst user) is significantly shorter than that of other users (secondand third users), throughput may deteriorate as compared with overhead(e.g., a PLCP, a training field and the like) for a system thatsimultaneously transmits a packet to multi-users (first to third users).Furthermore, overhead occurs in the first user due to a significant longMAC PAD 720 as compared with the second and third users. In order toreduce the overhead due to the MAC PAD 720, a ‘tail & PHY pad’ is addednext to the last bit of the final A-MPDU subframe 710-n (722). In such acase, the length of the packet is transmitted in units of bytes.

The above-mentioned problem of the overhead may also occur in the casein which a packet is transmitted to a single user, which will bedescribed with reference to FIG. 10. If the length of a packet istransmitted as the symbol number when transmitting the packet to asingle user, since VHT frame overhead and MAC pad overhead occur,throughput deterioration may occur. That is, a MPDU to be transmitted tothe single user is sent in the form of the A-MPDU subframe, resulting inthe occurrence of overhead (VHT frame overhead) due to the delimiter andthe 0˜3 pad included in the A-MPDU subframe, and the null delimeter 724and the final MAC pad 726 may be added in order to adjust the length ofthe packet in units of symbols, resulting in the occurrence of overhead(MAC frame overhead). Even when transmitting a single MPDU to the singleuser, the VHT frame overhead and the MAC frame overhead may occur. Thatis, this is because the transmission of the single MPDU represents thetransmission of a single A-MPDU subframe to a VHT A-MPDU 844 illustratedin FIG. 10.

In this regard, the embodiment of the present invention proposes amethod for transferring the length of a packet to be transmitted to eachuser using the same field in units of bytes or symbols in order to theabove-mentioned overhead when simultaneously transmitting a packet toone or more users.

Whether the length of the packet to be transmitted to each user istransferred in units of bytes or symbols can be determined according tovarious criteria. For example, when transmitting data (e.g., a singleMPDU) with a length shorter than a specific length, a special managementframe (e.g., various frames necessary for managing a wirelesscommunication system), or a single MPDU due to the impossibility ofaggregation, the length information of a packet can be transferred inunits of bytes instead of the symbol number. In this way, the MAC padoverhead can be reduced. Furthermore, when trying to improve thethroughput through data aggregation, the length of a packet can betransferred as the symbol number.

The case in which a packet is transmitted to a single user and the casein which packets are transmitted to multi-users including two or moreusers will be described below. When transmitting the packet to thesingle user, the length information of the packet may be transferred inunits of bytes. This is because it is possible to reduce the MAC padoverhead necessary in order to adjust the length of the packet in unitsof bytes. Meanwhile, when simultaneously transmitting packets to themulti-users, the length information of the packets may be transferred inunits of symbols or bytes according to the lengths of the packets to betransmitted to each user. That is, if the lengths of the packets to betransmitted to each user are transferred in units of symbols, sinceoverhead occurs (e.g., refer to FIG. 9), the lengths of the packets maybe transferred to a user, which receives a packet with a short length,in units of bytes, and the lengths of the packets may be transferred toa user, which receives a packet with a long length, in units of symbols.For example, the lengths of the packets may be transferred to a user inunits of bytes, which receives data (e.g., a single MPDU) with a lengthshorter than a specific length or a special management frame, and thelengths of the packets may be transferred to a user in units of symbols,which receives data with a length longer than a specific length or dataaggregated in order to improve the throughput.

The length information of the packet, which may be expressed by twounits (in units of bytes or symbols), may be included in a field (810,e.g., the L-SIG 814) for legacy, a common field (820, e.g., the VHT-SIGs822) for VHT, or a field (830, e.g., a signal field for each user of theVHT) for each user of the VHT, and the position thereof is not limited.The packet length information on each user may be included in the field830 for each user of the VHT, but may be included in the common field820. When the packet length information on each user is included in thecommon field, length information on each user may be included thereintogether with information on each user.

Since the wireless communication system in accordance with theembodiment of the present invention includes the length field in thelegacy signal field (814: L-SIG) in order to achieve compatibility withlegacy systems, a method for expressing length information of a packetin the range of the length field will be described as an example. Thelength field in the legacy signal field (814: L-SIG) is 12 bits. Themaximum number of bytes, which can be expressed using the length fieldof 12 bits, is 4095, and the maximum transmission duration based on themaximum number of bytes cannot exceed 5.5 ms or more according to theL-SIG TXOP protection technology defined in 802.11n. Hereinafter, amethod for expressing the transmission duration information (in units ofsymbols) or byte length information (in units of bytes) of a packetusing 12 bits (1100) will be described with reference to FIG. 11.

A single MPDU includes data with the maximum length of 2304 bytes and aMAC header and has a length of 2400 bytes or less. Thus, the byte lengthinformation of the single MPDU can be expressed by 12 bits. In detail,the maximum length of the single MPDU does not exceed a value of ‘11000000 0000’ bytes. Furthermore, the defined maximum TXOP length is 3.008ms, can be expressed by 12 bits, and in detail, is equal to or less than‘0011 1111 1111’. Thus, when 2 bits (1110) of the 12 bits (1100) are‘11’ (11xx xxxx xxxx), the length field represents transmission durationinformation, that is, a transmission symbol number of a packet (refer to(a) of FIG. 11). A part 1120, except for the 2 bits (1110), representsthe transmission symbol number of the packet. When the 2 bits (1110) ofthe 12 bits (1100) are not ‘11’ (10xx xxxx xxxx, 01xx xxxx xxxx, 00xxxxxx xxxx), the length field represents byte length information (referto (b), (c), and (d) of FIG. 11). Here, a part 1100 represents the bytelength of the packet.

So far, the case in which the length field is 12 bits has been describedas an example. However, the present invention is not limited thereto.That is, the length field representing the length information of apacket in accordance with the embodiment of the present invention mayinclude an indication field representing a byte-unit packet length or asymbol-unit packet length, and represent the length of the packet usingthe whole or a part (e.g., a field except for the indication field) ofthe length field. The indication field may be 1 bit or more.Consequently, a receiver of the packet can recognize the unit (a byteunit or a symbol unit) of length information through the indicationfield in the length field representing the length information of thepacket, and also recognize the length of the packet according thecorresponding unit using the whole or the part (e.g., the field exceptfor the indication field) of the length field based on the unit oflength information.

The field representing the length information of a packet is expressedby two units in accordance with the embodiment of the present invention,so that the efficiency of the system can be improved. For example, inthe case of data transmission of a specific length or less such as asingle MPDU, since data is transmitted in a byte-length, it is possibleto reduce unnecessary overhead such as pad overhead. Furthermore, aSU-MIMO (single user MIMO) and a MU-MIMO (multi-user MIMO) can use thesame packet structure.

So far, the case in which the length information of a packet transmittedto each user is represented has been described. However, the maximumlength information of a packet transmitted to multi-users can berepresented by the method in accordance with the embodiment of thepresent invention. At this time, the maximum length information of thepacket transmitted to the multi-users can be transferred through thecommon field 820, the length information of the packet transmitted toeach user can be transferred through the field 830 for each user, andthe two pieces of information can be transferred.

Hereinafter, the configurations of a packet transmitter 1210 capable ofsimultaneously transmitting packets to one or more users and a packetreceiver 1220 capable of receiving and processing such packets from thepacket transmitter 1210 according to the above-described method will bedescribed with reference to FIG. 12. Here, the duplicated descriptionsas described above will be omitted. An AP and an STA of a wirelesscommunication system may serve as a packet transmitter or packetreceiver.

The packet transmitter 1210 includes a packet generation unit 1212 and atransmission unit 1214.

The packet generation unit 1212 is configured to generate packets to betransmitted to one or more users according to the above-describedmethod.

The transmission unit 1214 is configured to simultaneously transmit thepackets generated by the packet generation unit 1212 to the one or moreusers (the packet receiver 1220).

The packet receiver 1220 includes a reception unit 1224 and a packetprocessing unit 1222.

The reception unit 1224 is configured to receive the packet from thepacket transmitter 1210, and the packet processing unit 1222 isconfigured to process the packet received in the reception unit 1224according to the above-described method.

In accordance with the embodiment of the present invention, whensimultaneously transmitting/receiving packets with different lengthsto/from multi-users, a packet with a length shorter than a maximumpacket length can be correctly processed, thereby reducing unnecessaryoverhead.

Furthermore, in accordance with the embodiment of the present invention,even when transmitting a packet to a single user, it is possible toreduce unnecessary overhead.

In addition, since the VHT A-MPDU frame defined in the embodiment of thepresent invention basically maintains the A-MPDU frame structure and thePSDU structure of the PHY which are defined in 802.11n, the VHT A-MPDUframe can be easily applied without a specific change in the structurethereof.

Moreover, since the multi-antenna technology for supporting multi-userscan be dynamically configured according to services based on thewireless communication system proposed in the embodiment of the presentinvention, various services can be supported and the throughputimprovement effect can be expected.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A method for simultaneously transmitting packets to one or more usersin a wireless communication system, the method comprising: generatingthe packets which include length information and are to be transmittedto the one or more users; and simultaneously transmitting the generatedpackets to the one or more users, wherein the length informationincludes information representing a unit of the length information andinformation representing lengths of the packets according to the unit.2. The method of claim 1, wherein the unit of the length information isa byte or a symbol.
 3. The method of claim 2, wherein, when transmittingthe packet to the one user, the unit of the length information isdetermined as the byte, and when transmitting the packets to two or moreusers, the unit of the length information is determined as the byte iflengths of the packets to be transmitted to each of the two or moreusers are shorter than a predetermined length while being determined asthe symbol if the lengths of the packets to be transmitted to each ofthe two or more users are longer than the predetermined length.
 4. Themethod of claim 2, wherein the length information is included in alength field in a legacy signal field, the information representing theunit of the length information is included in 2 bits from a mostsignificant bit of the length field, the unit of the length informationis the symbol and the information representing the lengths of thepackets is included in a part except for the 2 bits from the lengthfield when a value of the 2 bits is ‘11’, and the unit of the lengthinformation is the byte and the information representing the lengths ofthe packets is included in a whole of the length field when the value ofthe 2 bits is one of ‘10’, ‘01’ and ‘00’.
 5. A method for receiving apacket from a transmitter which simultaneously transmits packets to oneor more users in a wireless communication system, the method comprising:receiving a packet including length information of the packet; andprocessing the packet using the length information of the receivedpacket, wherein the length information includes information representinga unit of the length information and information representing lengths ofthe packets according to the unit.
 6. The method of claim 5, wherein theunit of the length information is a byte or a symbol.
 7. The method ofclaim 6, wherein the length information is included in a length field ina legacy signal field, the information representing the unit of thelength information is included in 2 bits from a most significant bit ofthe length field, the unit of the length information is the symbol andthe information representing the lengths of the packets is included in apart except for the 2 bits from the length field when a value of the 2bits is ‘11’, and the unit of the length information is the byte and theinformation representing the lengths of the packets is included in awhole of the length field when the value of the 2 bits is one of ‘10’,‘01’ and ‘00’.
 8. An apparatus for simultaneously transmitting packetsto one or more users in a wireless communication system, the apparatuscomprising: a packet generation unit configured to generate packetswhich include length information and are to be transmitted to the one ormore users; and a transmission unit configured to simultaneouslytransmit the generated packets to the one or more users, wherein thelength information includes information representing a unit of thelength information and information representing lengths of the packetsaccording to the unit.
 9. The apparatus of claim 8, wherein the unit ofthe length information is a byte or a symbol.
 10. The apparatus of claim9, wherein, when transmitting the packet to the one user, the unit ofthe length information is determined as the byte, and when transmittingthe packets to two or more users, the unit of the length information isdetermined as the byte if lengths of the packets to be transmitted toeach of the two or more users are shorter than a predetermined lengthwhile being determined as the symbol if the lengths of the packets to betransmitted to each of the two or more users are longer than thepredetermined length.
 11. The apparatus of claim 9, wherein the lengthinformation is included in a length field in a legacy signal field, theinformation representing the unit of the length information is includedin 2 bits from a most significant bit of the length field, the unit ofthe length information is the symbol and the information representingthe lengths of the packets is included in a part except for the 2 bitsfrom the length field when a value of the 2 bits is ‘11’, and the unitof the length information is the byte and the information representingthe lengths of the packets is included in a whole of the length fieldwhen the value of the 2 bits is one of ‘10’, ‘01’ and ‘00’.
 12. Anapparatus for receiving a packet from a transmitter which simultaneouslytransmits packets to one or more users in a wireless communicationsystem, the apparatus comprising: a reception unit configured to receivea packet including length information of the packet; and a packetprocessing unit configured to process the packet using the lengthinformation of the received packet, wherein the length informationincludes information representing a unit of the length information andinformation representing lengths of the packets according to the unit.13. The apparatus of claim 12, wherein the unit of the lengthinformation is a byte or a symbol.
 14. The apparatus of claim 13,wherein the length information is included in a length field in a legacysignal field, the information representing the unit of the lengthinformation is included in 2 bits from a most significant bit of thelength field, the unit of the length information is the symbol and theinformation representing the lengths of the packets is included in apart except for the 2 bits from the length field when a value of the 2bits is ‘11’, and the unit of the length information is the byte and theinformation representing the lengths of the packets is included in awhole of the length field when the value of the 2 bits is one of ‘10’,‘01’ and ‘00’.